I've opened up a ZX81 I bought as not working on eBay and found the following user modification to the RAM.

I am assuming that the original owner has (tried to) upgrade the internal RAM but I cannot see how the modifications that they have made correspond to the internal RAM upgrades I have read about elsewhere.

Does anyone have any ideas as to what kind of RAM upgrade this might be and whether or not it looks like it should work. From what I've read it looks as if some of the pins should have been bent up but I am just guessing.

It is possible that this is a botched upgrade and that this is the reason why the machine does not work. I don't know. I don't even know for certain that the machine does not work as I have not applied power yet or made any other tests. I wanted to inspect visually to see if there were any obvious issues with the motherboard before I did so and found this which baffles me (but being new to this, many things baffle me so I thought it wisest to ask!).

Thanks in advance for any suggestions.

(I took these photos earlier and am not in front of the machine right now so I'll have to take any suggestions in batches and do them all at once when I next get time to sit down to do so. I will update this thread with any new information as and when I get a chance to investigate further.)

Thank you. That is amazingly helpful. Is the site you link to yours? Those pictures are very useful.

Next time I get a chance to sit down with it, I am going to risk powering it on and then, if there is no display, start investigating further. Now that I know what this mod is supposed to be doing, I'll have a better chance of working out if it is working as intended.

Thank you. That is amazingly helpful. Is the site you link to yours? Those pictures are very useful.

Next time I get a chance to sit down with it, I am going to risk powering it on and then, if there is no display, start investigating further. Now that I know what this mod is supposed to be doing, I'll have a better chance of working out if it is working as intended.

I'll keep you posted on my progress.

(And thank you for your welcome on the other thread too!)

You are welcome! No the site isn’t mine. I am ok at following other peoples instructions and expertise but not in coming up with ways to do these things! I am also familiar with lifted tracks when modding these things.

Has it been composite modded? Daft as it sounds I sold one (of quite a few) on eBay where I had done the RAM as shown and fitted a ZX8-CCB composite mod board and the buyer got in touch to say it didn’t work. He had tried to plug it into the RF input of the telly and not a composite socket! Once plugged into the correct socket all was well.
After that I always bundled a composite to SCART adaptor with them to be sure it was plugged in correctly.